Behavioural sensitization in 6-hydroxydopamine lesioned rats involves the dopamine signal transduction: Changes in DARPP-32 phosphorylation

Abstract

“Priming” is a phenomenon of behavioural sensitization observed in unilaterally 6-hydroxydopamine lesioned rats following exposure to a dopamine agonist. After priming, a single dose of the D 1 agonist SKF 38393 (3 mg/kg) produces contralateral turning, while the same dose is inactive in drug-naive, lesioned animals. The molecular mechanisms of “priming” were investigated here by studying the phosphorylation of dopamine and adenosine 3′–5′ monophosphate regulated phosphoprotein (DARPP32), a dopamine- and cyclic AMP-regulated phosphoprotein functionally linked to D 1 receptors in striatum. Dephospho-form of DARPP-32 was measured by a back-phosphorylation assay. All assays were performed in striata from both lesioned and unlesioned sides. A significant decrease of dephosphoDARPP-32 (27%) was observed in the denervated striatum of primed rats, indicating an increased Phosphorylation in vivo of DARPP-32 in response to the D 1 agonist. The levels of DARPP-32 protein, as measured by quantitative immunoblotting, remained unchanged in all experimental groups. This study shows that priming is expressed as an increased transduction of the D 1 receptor message.